Slag is a by-product of metal production processes conducted in metallurgical furnaces. During metal production, slag is present in the metallurgical furnace in molten form. Molten slag is periodically or continuously tapped from the furnace for disposal and/or further processing. Inevitably the tapped slag stream will contain one or more metal values, including entrained particles or droplets of molten metal which have been produced in the furnace. Although measures may be taken to reduce the loss of metal values in the molten slag stream, such measures are only partly successful. As a result, the entrainment of metals represents a loss ranging from 0.1 to 5% (typically about 1-2%) of the metal produced in the furnace. Additionally, in some specific operations, inefficiency and/or poor operational control can result in discrete events which result in large volumes of metal being lost to the slag stream.
The slag stream may also contain one or more other metal values, which could be extracted in the downstream operations as by-products of the process. In some cases these metallic by-products may be of significant value.
Once it is tapped, the molten slag is typically allowed to cool and solidify in large masses. Recovery of metal values from the solidified slag is extremely difficult and costly due to the need for handling the large masses of solidified material, and crushing the material to a size which makes metal recovery possible through any physical or chemical process.
For example, one common separation method includes the steps of: 1) transporting and dumping the slag; 2) natural cooling and solidification or in some cases use of water spray to accelerate the cooling process; 3) crushing and grinding the solidified slag; and 4) magnetic separation. However, there are several problems associated with this method, including: the need for significant space for dumping and cooling of the slag; safety concerns due to transporting large volumes of slag to the dumping area; the risk of explosion from spraying water on the molten slag; and dust creation during the crushing/grinding process. Furthermore, the recovery of non-magnetic metals/alloys such as FeMn is even more complicated.
There remains a need for effective processes and apparatus for recovery of entrained metals and/or metal by-products from molten slag streams, which avoid the difficulties and costs associated with handling and crushing of solidified slag.